1. Field of the Invention:
The present invention relates to a lithium-ion conducting solid electrolyte. More particularly, it relates to a lithium-ion conducting solid electrolytes that are used in solid-state electrical/chemical elements such as solid-state batteries, solid electrolyte double-layered capacitors, solid electrochromic displays, and the like.
2. Description of the Prior Art:
In recent years, the progress in technology of electronic industries is remarkable. Electronic devices such as integrated circuits (IC), large scaled integrated circuits (LSI), and the like are used in various fields to make electronic apparatus smaller and thinner. However, diminishment in size of conventional electrical/chemical elements that include electrolytic solution is limited, because sealing of the elements requires highly advanced techniques and the proportion of sealing materials in them become larger as they are diminished in size. In contrast to the conventional elements, solid-state electrical/chemical elements, which consist of solid components can be diminished in size readily, because in such solid elements, the seal is not needed. Solid electrolytes, solid-state ion conductors that can transport ions, are essential for constructing such solid-state elements and thus new materials for solid electrolytes are now being developed.
One example is the application of lithium-ion conducting polyelectrolyte, which can be processed readily and has flexibility, to batteries and the like. Typical example of this is poly(oligooxyethylene methacrylate)-alkaline metal system, although it is still under investigation, because of several problems. The problems are that the maximum ionic conductivity of the system, which is about 10.sup.-5 S/cm, does not reach the level required for practical use and that not only cation (Li.sup.+), but also anions (e.g. ClO.sub.4.sup.-) are transported in the system. Further, this polyelectrolyte is reactive with a lithium metal that is used for an anode.
As for inorganic lithium-ion conducting solid electrolytes, of which conductivities are about 10.sup.-3 S/cm, LiI--Li.sub.2 S--X (wherein X is at least one sulfide selected from the group consisting of B.sub.2 S.sub.3, SiS.sub.2, P.sub.2 S.sub.5, Al.sub.2 S.sub.3, and GeS.sub.2) and Li.sub.3 N system are well known. However, they are not put to practical use, because their decomposition voltages are below 3.0 V.